Antiperspirant compositions are generally applied to an axillary region to limit perspiration and/or to limit or kill bacteria in this region. In this way, body odor caused by bacterial growth is limited or at least reduced.
Antiperspirants can be delivered topically in liquid form including by roll-on or, as an aerosol. When these compositions are applied to the axillary region, solvent evaporates to leave an active antiperspirant ingredient on the skin.
Active antiperspirant ingredients are well known in the art and often comprise an aluminum-containing salt.
Aluminum containing antiperspirant actives (for example, aluminum chlorohydrex and aluminum zirconium glycine salts) are known to contain a variety of polymeric and oligomeric species. It has been clinically shown that in general, the smaller the species, the higher the efficacy for reducing perspiration.
Size exclusion chromatography (“SEC”) is a method frequently used for obtaining information on polymer distribution in antiperspirant salt solutions. With appropriate chromatographic columns, generally five distinctive groups of polymer species can be detected in commercial aluminum and aluminum-zirconium complexes. These appear in a chromatogram as peaks 1, 2, 3, 4 and 5, respectively. Peak 1 contains the larger zirconium species (greater than 60 Angstroms). Peaks 2 and 3 contain the larger aluminum species. Peak 4 contains smaller aluminum species (aluminum oligomers, or small aluminum clusters) and these species have been correlated with enhanced efficacy for both aluminum and aluminum/zirconium salts. Peak 5 contains the smallest and most acidic aluminum species.
Due to the high efficacy of Peak 4 species, aluminum salts comprising a high proportion of Peak 4 species may be used in low amounts in antiperspirant compositions whilst maintaining an acceptable level of antiperspirant efficacy.
Ethylenediaminetetraacetic acid (EDTA) and its sodium salts are widely used in the cosmetic and personal care industry as chelating agents and/or preservation system boosters. In particular, tetrasodium EDTA is found in various antiperspirant roll-on formulations. Its aminopolycarboxylic structure of four acetate arms connected by two central amines allows strong hexadentate coordination to heavy metals. However, since aluminum-containing antiperspirant actives carry a large cationic charge, the strong interaction between EDTA and aluminum-containing antiperspirant actives may lead to an instability of the antiperspirant active within antiperspirant formulations, with a consequent loss in antiperspirant efficacy. As further discussed below, the instability is more pronounced in antiperspirant compositions comprising low levels of aluminum-containing antiperspirant actives.
It would therefore be desirable to stabilize aluminum salts in antiperspirant compositions comprising low levels of aluminum-containing salts, and prevent their instability and consequential loss in antiperspirant efficacy.